2011-01-28

Spirit Sol 736

Once again, I woke up in the middle of the night with an urgent desire to check on the drive ... and looked at the clock, decided not to make this a habit, and went back to sleep.

By the time I get in, Ashley and John have already roughed out the next drive. Yestersol's drive made about 26m of progress, stopping when autonav failed to find a path between Scylla and Charybdis (as we thought might happen). Still, this is a decent showing -- I think we might have actually caught up on our drive metric a bit (we're now 90m behind on that, maybe 170m from Home Plate) -- and we're ready for the next one.

And boy, are we ever ready for the next one. We got all the diagnostic data down, and Jeff Biesiadecki's call is that this is merely a recurrence of the previous Spirit steering anomaly. So we're good to ignore the dynamic brakes and resume normal driving. Triumph!

The original plan for the weekend had been to resume the autonav-only continuation-drive sols. But there's this rock smack dab in the middle of the IDD work volume .... It's not a big rock, only about 5cm tall and 12cm wide. But it's possibly a vesicular basalt, a rock type of particular interest to at least some of the science team. In particular, to Oded Aharonson. And since he's the SOWG chair today, there'll be at least one voice calling for a change of plans.

I'd like to be able to argue that we should blow it off and drive. But when Oded asks, I have to admit that the autonav-only sols haven't been performing well. Let's be generous and figure that we might make as much as 40m from a two-hour autonav-only drive. But if the first sol stops because autonav can't find a safe path, the second won't even try to move. Given the increasingly rocky terrain we're in (it looks like we're seeing another ejecta blanket), I figure there's about a 70% chance of no progress at all on the second sol. Which really means we're giving up only about 30% of 40m, or about 12m -- and that's using generous assumptions.

With those numbers in front of him, Oded can't resist the rock. Though the matter is unusually contentious at the SOWG meeting, with a number of the science folks saying we should skip the thing. (Justin is particularly vocal, and characteristically stubborn. At one point I suggest we let him name the rock; that idea gets a big laugh.) We have time only for MB or APXS, not both, and the results from only one of these instruments are a lot less scientifically valuable than the results from both together. Oded, however, makes the point that we mostly want this thing for the MI images -- morphology is the key to a vesicular basalt, more than chemistry -- and he gets his way in the end.

It's a more than usually tough sol. John and Ashley worry about the drive, while Terry and I take care of the IDD sequencing. IDDing this rock is just plain tricky: we want to try to get four MI stacks on it, but its small size makes that awkward. The least dusty and therefore most desirable face is toward us -- not on top -- so as the IDD gets close enough to plant an instrument on the rock, the hardware slides uncomfortably close to the ground. Worse, the rock is more or less rounded on top -- kind of like a half-buried football -- so that as we raise the IDD to increase its clearance from the ground, we get much less rock in the instrument's field of view. If only it were a LEGO brick.

The other tricky part is that the face we're poking at is fairly irregular, so that a simple linear mosaic won't do; we need to customize each stack, and have a MB touch for each (each of which also needs to be carefully analyzed to ensure we won't smack into the ground). Oh, and the MB will contact the rock at its outer surface, but because it's a vesicular basalt, we want to see into the vesicles -- the holes -- so we want to take MI images as close as 11mm. Which means we get that much closer to the rock, and to the ground ....

But, what the heck, we make it. And by aggressively parallelizing the work, we finish the whole thing -- from start of SOWG to end of CAM -- in only about seven hours.